Volcanoes have shifted Asian rainfall

Nov 03, 2010

Large, explosive volcanoes such as Indonesia's Merapi (erupting here in 2006) have the potential to change weather patterns if their eruptions are big enough. Credit: NASA

Scientists have long known that large volcanic explosions can affect the weather by spewing particles that block solar energy and cool the air. Some suspect that extended "volcanic winters" from gigantic blowups helped kill off dinosaurs and Neanderthals. In the summer following Indonesia's 1815 Tambora eruption, frost wrecked crops as far off as New England, and the 1991 blowout of the Philippines' Mount Pinatubo lowered average global temperatures by 0.7 degrees F -- enough to mask the effects of manmade greenhouse gases for a year or so.

Now, scientists have shown that eruptions also affect rainfall over the Asian monsoon region, where seasonal storms water crops for nearly half of earth's population. Tree-ring researchers at Columbia University's Lamont-Doherty Earth Observatory showed that big eruptions tend to dry up much of central Asia, but bring more rain to southeast Asian countries including Vietnam, Laos, Cambodia, Thailand and Myanmarthe opposite of what many climate models predict. Their paper appears in an advance online version of the journal Geophysical Research Letters.

The growth rings of some tree species can be correlated with rainfall, and the observatory's Tree Ring Lab used rings from some 300 sites across Asia to measure the effects of 54 eruptions going back about 800 years. The data came from Lamont's new 1,000-year tree-ring atlas of Asian weather, which has already produced evidence of long, devastating droughts; the researchers also have done a prior study of volcanic cooling in the tropics. "We might think of the study of the solid earth and the atmosphere as two different things, but really everything in the system is interconnected," said Kevin Anchukaitis, the study's lead author. "Volcanoes can be important players in climate over time."

Large explosive eruptions send up sulfur compounds that turn into tiny sulfate particles high into the atmosphere, where they deflect solar radiation. Resulting cooling on earth's surface can last for months or years. (Not all eruptions will do it; for instance, the continuing eruption of Indonesia's Merapi this fall has killed dozens, but this latest episode is probably not big enough by itself to effect large-scale weather changes.) As for rainfall, in the simplest models, lowered temperatures decrease evaporation of water from the surface into the air; and less water vapor translates to less rain. But matters are greatly complicated by atmospheric circulation patterns, cyclic changes in temperatures over the oceans, and the shapes of land masses. Up to now, most climate models incorporating known forces such as changes in the sun and atmosphere have predicted that volcanic explosions would disrupt the monsoon by bringing less rain to southeast Asia--but the researchers found the opposite.

This photo shows an 18-kilometer-high plume from one of a series of eruptions in 1991 at Mount Pinatubo. Credit: USGS

The researchers studied eruptions including one in 1258 from an unknown tropical site, thought to be the largest of the last millennium; the 1600-1601 eruption of Peru's Huaynaputina; Tambora in 1815; the 1883 explosion of Indonesia's Krakatau; Mexico's El Chichón, in 1982; and Pinatubo. The tree rings showed that huge swaths of southern China, Mongolia and surrounding areas consistently dried up in the year or two following big events, while mainland southeast Asia got increased rain. The researchers say there are many possible factors involved, and it would speculative at this point to say exactly why it works this way.

"The data only recently became available to test the models," said Rosanne D'Arrigo, one of the study's coauthors. "Now, it's obvious there's a lot of work to be done to understand how all these different forces interact." For instance, in some episodes pinpointed by the study, it appears that strong cycles of the El Niño-Southern Oscillation, which drives temperatures over the Pacific and Indian oceans and is thought to strongly affect the Asian monsoon, might have counteracted eruptions, lessening their drying or moistening effects. But it could work the other way, too, said Anchukaitis; if atmospheric dynamics and volcanic eruptions come together with the right timing, they could reinforce one another, with drastic results. "Then you get flooding or drought, and neither flooding nor drought is good for the people living in those regions," he said. The study also raises questions whether proposed "geoengineering" schemes to counteract manmade climate change with huge artificial releases of volcanism-like particles might have complex unintended consequences.

Ultimately, said Anchukaitis, such studies should help scientists refine models of how natural and manmade forces might act together to in the future to shift weather patternsa vital question for all areas of the world.

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Good Grief! This is the first time I have ever been able to completely agree with a comment from marjon. Marjon, I agree with your observation on geo-engineering. It concerns me when people jump on the idea of pumping thousands of tons of nano-SO2 into the atmosphere without understanding the consequences.

Do nothing is also a political decision So you don't really care about the unintended climatic and subsequent economic consequences ?

Climate changes.The best response is to have a robust economic system that can quickly adapt to changing conditions. Govt controlled economies have been proven to be rigid. The IPCC and AGWites advocate a more govt controlled, rigid economy.

If you mean old-style nuclear power, there's no good reason to support it (it's expensive, it's dangerous, it creates long-lasting pollution, and it poses weapons proliferation concerns.)

As for new tech that is supposedly cheaper, safer, more efficient, has no appreciable weaponization potential, and produces only short-lived waste in small quantities: sadly, so far it only exists on paper. I'm all for R&D, but it's far from ready for deployment: gen 3 reactors are just starting to tentatively appear (being little more but evolutionary incremental improvements on old designs); gen 4's everyone loves to tout (e.g. Thorium breeders) are 15-20 years out even by optimistic projections.

And even then, nuke plants only provide centralized grid-oriented power sources; I'd prefer a healthy balance between centralized and local power (the latter would be wind/solar/geothermal/biofuel/renewable hydrogen + fuel cells etc.

"Manufacturers of refrigerator-sized nuclear reactors will seek approval from U.S. authorities within a year to help supply the world’s growing electricity demand. ""Small reactors have been used in U.S. submarines since the USS Nautilus was commissioned in 1954.""Deal, a licensed Christian minister and self-confessed “left-wing nutbag” who only began to support nuclear power four years ago, says the simplicity and scale of his reactor can overcome concerns about waste and terrorism. "http://www.bloomb...ket.html

"A nuclear reactor designed to generate power in the basement of an apartment block is being developed in Japan. In the past few months government-backed researchers have been testing a fail-safe mechanism for the reactor, which will close down automatically if it overheats. "http://www.inters...216.html

That's nice, but nukes are only economical when they are large-scale. Then you can develop high heat gradients, and utilize highly efficient mega-turbines. I suspect that for something that's refrigerator-sized, you're going to pay more than for the rest of your house. NASA's had compact RTG's since the 60's; they'll only ding you for a couple million each, but you'll have enough power to run a couple of light bulbs...

Everyone's main pet peeve about renewables like solar cells, is that they're too expensive compared to cheap electricity from the grid. Well, they're peanuts compared to a personal (or even neighborhood-scale) nuclear reactor.